Hydraulic steering arrangement

ABSTRACT

A hydraulic steering arrangement ( 2 ) is described having a main flow path ( 8 ) with a flow meter ( 9 ) and an amplification flow path ( 10 ) opening into the main flow path ( 8 ) at a connecting point ( 11 ) located between the flow meter ( 9 ) and a working port arrangement (L, R). Such a steering arrangement should have in a simple way a large flow of the hydraulic fluid to the working port arrangement. To this end pressure increasing means ( 17 ) are arranged in the main flow path ( 8 ) upstream the connecting point ( 11 ).

CROSS-REFERENCE TO RELATED APPLICATION

This application claims foreign priority benefits under U.S.C. § 119 toGerman Patent Application No. 10 2017 100 186.7 filed on Jan. 6, 2017,the content of which is hereby incorporated by reference in itsentirety.

TECHNICAL FIELD

The present invention relates to a hydraulic steering arrangement havinga main flow path with a flow meter and an amplification flow pathopening into the main flow path at a connecting point located betweenthe flow meter and a working port arrangement.

BACKGROUND ART

Such a steering arrangement is known, for example, from EP 2 786 915 B1.

When a vehicle equipped with such a steering arrangement is steered, thedriver turns a steering wheel (or any other command means). By turningthe steering wheel two elements, in particular a spool and a sleeve, aremoved relatively to each other to open a number of orifices in the mainflow path. This allows a certain amount of hydraulic fluid to pass themain flow path. This hydraulic fluid drives the flow meter which in turnrestores the initial relative positions of the two elements. Therefore,when the steered wheels have reached the position commanded by thesteering wheel the main flow path is closed again.

In order to deliver more hydraulic fluid to the steering motor connectedto the working port arrangement the amplification flow path is used. Inthe amplification flow path an orifice, so called amplification orifice,is arranged which is opened and closed in synchronism with the orificesin the main flow path. Therefore, an additional flow proportional to theflow through the main flow path can be guided through to theamplification flow path. However, even with such a hydraulic steeringarrangement it is in some cases difficult to satisfy the requirements ofa desired steering velocity. In particular, when a steering motorconnected to the working port arrangement has a big displacement, likein big articulated steered vehicles, it is difficult to supply thenecessary amount of hydraulic fluid to the steering motor.

SUMMARY

An object underlying the invention is to have in a simple way a largeflow of hydraulic fluid to the working port arrangement.

This object is solved with a hydraulic steering arrangement as describedat the outset in that pressure increasing means are arranged in the mainflow path upstream the connecting point.

When the flow path comprises pressure increasing means the pressure dropbetween a supply port and the connecting point is increased. Thispressure drop drives the hydraulic fluid through the main flow path. Thesame pressure drop drives the hydraulic fluid through the amplificationflow path as well. The higher the pressure drop is, the more hydraulicfluid is driven through the amplification flow path so that at the end alarger amount of hydraulic fluid is supplied to the working portarrangement.

In an embodiment of the invention the pressure increasing means arelocated downstream the flow meter. In other words, the pressureincreasing means are located between the flow meter and the connectingpoint.

In an embodiment of the invention the pressure increasing means arelocated downstream a flow meter orifice. In many cases two flow meterorifices are located near the flow meter, one flow meter orificeupstream and one flow meter orifice downstream the flow meter. When thepressure increasing means are located downstream the flow meter orifice,it is kept outside of the neighborhood of the flow meter.

In an embodiment of the invention the pressure increasing means arelocated upstream the last orifice in the main flow path. The combinedflow through the main flow path and through the amplification flow pathis controlled by the last orifice.

In an embodiment of the invention the pressure increasing means are inform of a flow resistance. When hydraulic fluid passes the flowresistance, a certain pressure is necessary to drive the hydraulic fluidthrough the flow resistance. The higher the flow resistance is, thegreater is the pressure needed. This pressure is supplied by a pressuresource, for example, a hydraulic pump driven by the motor of thevehicle. This pump is in many cases pressure controlled or, in analternative, pressure control means are arranged between the pump andthe steering arrangement. When the pressure or the flow resistance hasto be increased, a higher pressure from the pump is used.

In an embodiment of the invention the flow resistance is in form of anorifice. This is a simple way to realize a hydraulic flow resistance.

In an embodiment of the invention the orifice is a variable orifice.

In an embodiment the flow resistance of the variable orifice changesproportionally with a change of flow resistance of a main orifice in themain flow path.

In an alternative embodiment of the invention the orifice is a fixedorifice.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described in more detail withreference to the drawing, wherein the only FIGURE is a schematicillustration of a hydraulic steering arrangement.

DETAILED DESCRIPTION

A hydraulic steering 1 of a vehicle comprises a hydraulic steeringarrangement 2, a steering motor 3 and a pressure source 4. The pressuresource 4 comprises a pump 5 and/or a priority valve 6 which makes itpossible to adjust the pressure delivered by the pressure source 4. Thepump 5 is connected to a tank 7. Hydraulic fluid returning from thesteering motor 3 is guided back to the tank 7.

The hydraulic steering arrangement 2 comprises a main flow path 8 inwhich a flow meter 9 and a number of orifices are arranged.

In a direction from the pressure source 4 to the steering motor 3 thereis a main orifice A1, a first flow meter orifice A2 upstream the flowmeter 9, a second flow meter orifice A3 downstream the flow meter 9 anda further orifice A4 upstream the steering motor 3.

An amplification flow path 10 runs parallel to the main flow path 8 andopens into the main flow path 8 at a connecting point 11 arrangedupstream the last mentioned orifice A4. An amplification orifice AU isarranged in the amplification flow path 10.

A load sensing line 12 is connected to the priority valve 6 via anorifice ALS. The load sensing line 12 is connected to the tank 7 bymeans of an overpressure valve 13.

Furthermore, a control valve 14 is arranged within the load sensing line12 throttling a flow through the load sensing line 12 from a point 15between the main orifice A1 and the first flow meter orifice A2 to thetank. The degree of throttling is determined by a control pressurewithin said steering arrangement 2. This control pressure is in thepresent embodiment the pressure at the mentioned point 15 between themain orifice A1 and the first flow meter orifice A2.

The steering arrangement 2 comprises a working port arrangement L, R, asupply port P and a return port T. The FIGURE shows a situation in whichthe left working port L is supplied with hydraulic fluid and fluidreturning from the steering motor 3 is returned via the right workingport R and a return line 16 to tank. A variable orifice A5 is arrangedin the return line 16. A further variable orifice Adrain is arrangedbetween the return line 16 and point 15 between the main orifice A1 andthe first flow meter orifice A2. However, it depends on the direction ofrotation of a steering wheel or the like which of the two working portsL, R is receiving hydraulic fluid under pressure and which of theworking ports R, L is returning hydraulic fluid back to the tank 7.

Furthermore, pressure increasing means 17 are arranged in the main flowpath 8 upstream the connecting point 11 and downstream the flow meter 9,in particular downstream the second flow meter orifice A3. The pressureincreasing means 17 are in form of a flow resistance. A simple way torealize such a flow resistance is the use of an orifice At. In thepresent embodiment this orifice At is a fixed orifice. It is, however,also possible to use a variable orifice in which the opening degree andtherefore the flow resistance depends on the opening degree and the flowresistance of the main orifice A1, for example.

When the steering wheel (not shown) or any other command means to steera vehicle is in a neutral position, all variable orifices except thedrain orifice Adrain are closed. The drain orifice Adrain is open. Whenthe steering wheel is turned, the main orifice A1 is opened and thedrain orifice Adrain is closed. Furthermore, the other variable orificesA2, A3, A4, A5, AU are opened. Hydraulic fluid entering the flow meter 9moves the flow meter 9 which in turn restores the orifices A1-A5, Adrainand Au to their initial condition.

Hydraulic fluid passing the main flow path 8 has to pass through thepressure increasing means 17 as well. The pressure increasing means 17increase a pressure drop between the supply port P and the connectingpoint 11. This pressure drop is as well responsible for driving thehydraulic fluid through the amplification path 10. The higher thispressure drop is, the more hydraulic fluid is driven through to theamplification flow path 10. The increase of pressure in the main flowpath 8 at point 15 is sensed by the load sensing line 12 which willtransmit this increased pressure to the priority valve 6. The priorityvalve 6 increases the pressure coming from the pump 5 and being suppliedto the pressure port P.

The connecting point 11 in which the amplification flow path 10 opensinto the main flow path 8 is located before the last orifice A4 so thatthe flow of hydraulic fluid through the amplification flow path 10 isinfluenced by the last orifice A4.

The orifices A4, A5 are dimensioned such that they are able to deal withthe larger flow of hydraulic fluid, i.e. with the combined flow of themain flow path 8 and of the amplification flow path 10.

While the present disclosure has been illustrated and described withrespect to a particular embodiment thereof, it should be appreciated bythose of ordinary skill in the art that various modifications to thisdisclosure may be made without departing from the spirit and scope ofthe present disclosure.

What is claimed is:
 1. A hydraulic steering arrangement having a mainflow path with a flow meter and an amplification flow path opening intothe main flow path at a connecting point located between the flow meterand a working port arrangement (L, R), wherein pressure increasing meansare arranged in the main flow path upstream the connecting point.
 2. Thesteering arrangement according to claim 1, wherein the pressureincreasing means are located downstream the flow meter.
 3. The steeringarrangement according to claim 2, wherein the pressure increasing meansare located downstream a flow meter orifice (A3).
 4. The steeringarrangement according to claim 3, wherein the pressure increasing meansare located upstream a last orifice (A4) in the main flow path.
 5. Thesteering arrangement according to claim 1, wherein the pressureincreasing means are in form of a flow resistance.
 6. The steeringarrangement according to claim 5, wherein the flow resistance is in formof an orifice (At).
 7. The steering arrangement according to claim 6,wherein the orifice is a variable orifice.
 8. The steering arrangementaccording to claim 7, wherein a flow resistance of the variable orificechanges proportionally with a change of flow resistance of a mainorifice (A1) in the main flow path.
 9. The steering arrangementaccording to claim 6, wherein the orifice (At) is a fixed orifice. 10.The steering arrangement according claim 2, wherein the pressureincreasing means are in form of a flow resistance.
 11. The steeringarrangement according claim 3, wherein the pressure increasing means arein form of a flow resistance.
 12. The steering arrangement accordingclaim 4, wherein the pressure increasing means are in form of a flowresistance.